Tunnel valve read sensor with crystalline alumina tunnel barrier deposited using room temperature techniques

ABSTRACT

In one general embodiment, a method includes forming a first magnetic layer, forming a tunnel barrier layer above the first magnetic layer, and forming a second magnetic layer above the tunnel barrier layer. The tunnel barrier layer includes crystalline alumina. The tunnel barrier layer is formed at a temperature of less than 100 degrees centigrade.

BACKGROUND

The present invention relates to data storage systems, and moreparticularly, this invention relates to a magnetic head with a tunnelvalve sensor having a crystalline alumina barrier layer.

In magnetic storage systems, magnetic transducers read data from andwrite data onto magnetic recording media. Data is written on themagnetic recording media by moving a magnetic recording transducer to aposition over the media where the data is to be stored. The magneticrecording transducer then generates a magnetic field, which encodes thedata into the magnetic media. Data is read from the media by similarlypositioning the magnetic read transducer and then sensing the magneticfield of the magnetic media. Read and write operations may beindependently synchronized with the movement of the media to ensure thatthe data can be read from and written to the desired location on themedia.

An important and continuing goal in the data storage industry is that ofincreasing the density of data stored on a medium. For tape storagesystems, that goal has led to increasing the track and linear bitdensity on recording tape, and decreasing the thickness of the magnetictape medium. However, the development of small footprint, higherperformance tape drive systems has created various problems in thedesign of a tape head assembly for use in such systems.

In a tape drive system, the drive moves the magnetic tape over thesurface of the tape head at high speed. Usually the tape head isdesigned to minimize the spacing between the head and the tape. Thespacing between the magnetic head and the magnetic tape is crucial andso goals in these systems are to have the recording gaps of thetransducers, which are the source of the magnetic recording flux in nearcontact with the tape to effect writing sharp transitions, and to havethe read elements in near contact with the tape to provide effectivecoupling of the magnetic field from the tape to the read elements.

SUMMARY

A method according to one embodiment includes forming a first magneticlayer, forming a tunnel barrier layer above the first magnetic layer,and forming a second magnetic layer above the tunnel barrier layer. Thetunnel barrier layer includes crystalline alumina. The tunnel barrierlayer is formed at a temperature of less than 100 degrees centigrade.

An apparatus, according to another embodiment, includes an array ofmagnetic tunnel junction devices arranged along a tape bearing surfaceof a magnetic tape head module, each magnetic tunnel junction devicehaving a reference layer, a free layer, and a tunnel barrier layerbetween the free and reference layers. The tunnel barrier layer of eachmagnetic tunnel junction device is primarily crystalline alumina. Inaddition, each tunnel barrier layer has a physical gradient in a degreeof crystallinity that increases from a bottom to a top thereof, with thehighest degree of crystallinity being at the top of the tunnel barrierlayer.

An apparatus according to yet another embodiment includes an array ofmagnetic tunnel junction devices arranged along a tape bearing surfaceof a magnetic tape head module, each magnetic tunnel junction devicehaving a reference layer, a free layer, and a tunnel barrier layerbetween the free and reference layers, where the tunnel barrier layer isprimarily crystalline alumina. In addition, an upper surface of the freelayer or reference layer under each tunnel barrier layer has physicalcharacteristics of being cleaned at a milling angle of between 40 and 80degrees for a duration sufficient to remove an amorphous native oxidesublayer therefrom. Moreover, the physical characteristics includeabsence of a metal oxide along the upper surface having an oxygen tometal ratio in the metal oxide that is outside an approximatelystoichiometric ratio.

Various embodiments may be implemented in a magnetic data storage systemsuch as a tape drive system, which may include a magnetic head, a drivemechanism for passing a magnetic medium (e.g., recording tape) over themagnetic head, and a controller electrically coupled to the magnetichead.

Other aspects and embodiments of the present invention will becomeapparent from the following detailed description, which, when taken inconjunction with the drawings, illustrate by way of example theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic diagram of a simplified tape drive systemaccording to one embodiment.

FIG. 1B is a schematic diagram of a tape cartridge according to oneembodiment.

FIG. 2 illustrates a side view of a flat-lapped, bi-directional,two-module magnetic tape head according to one embodiment.

FIG. 2A is a tape bearing surface view taken from Line 2A of FIG. 2.

FIG. 2B is a detailed view taken from Circle 2B of FIG. 2A.

FIG. 2C is a detailed view of a partial tape bearing surface of a pairof modules.

FIG. 3 is a partial tape bearing surface view of a magnetic head havinga write-read-write configuration.

FIG. 4 is a partial tape bearing surface view of a magnetic head havinga read-write-read configuration.

FIG. 5 is a side view of a magnetic tape head with three modulesaccording to one embodiment where the modules all generally lie alongabout parallel planes.

FIG. 6 is a side view of a magnetic tape head with three modules in atangent (angled) configuration.

FIG. 7 is a side view of a magnetic tape head with three modules in anoverwrap configuration.

FIG. 8 is a system diagram of an apparatus according to one embodiment.

FIG. 9 is a depiction of a tunneling magnetoresistive read sensorstructure according to one exemplary embodiment.

FIG. 10 is a flow diagram of a method for forming a magnetic tunneljunction structure according to one embodiment.

FIG. 11A is a magnified view of a graded CoFeAlO_(x) transition layer,according to one embodiment.

FIG. 11B is a Z-contrast image of the structure in FIG. 11A.

FIG. 11C is an electron energy loss spectroscopy (EELS) scan across theinterface shown in FIGS. 11A and 11B.

DETAILED DESCRIPTION

The following description is made for the purpose of illustrating thegeneral principles of the present invention and is not meant to limitthe inventive concepts claimed herein. Further, particular featuresdescribed herein can be used in combination with other describedfeatures in each of the various possible combinations and permutations.

Unless otherwise specifically defined herein, all terms are to be giventheir broadest possible interpretation including meanings implied fromthe specification as well as meanings understood by those skilled in theart and/or as defined in dictionaries, treatises, etc.

It must also be noted that, as used in the specification and theappended claims, the singular forms “a,” “an” and “the” include pluralreferents unless otherwise specified.

The following description discloses several preferred embodiments ofmagnetic storage systems, as well as operation and/or component partsthereof. Various embodiments include a magnetic head with a tunnel valvesensor having a crystalline alumina barrier layer.

In one general embodiment, a method includes forming a first magneticlayer, forming a tunnel barrier layer above the first magnetic layer,and forming a second magnetic layer above the tunnel barrier layer. Thetunnel barrier layer includes crystalline alumina. The tunnel barrierlayer is formed at a temperature of less than 100 degrees centigrade.

In another general embodiment, an apparatus includes an array ofmagnetic tunnel junction devices arranged along a tape bearing surfaceof a magnetic tape head module, each magnetic tunnel junction devicehaving a reference layer, a free layer, and a tunnel barrier layerbetween the free and reference layers. The tunnel barrier layer of eachmagnetic tunnel junction device is primarily crystalline alumina. Inaddition, each tunnel barrier layer has a physical gradient in a degreeof crystallinity that increases from a bottom to a top thereof, with thehighest degree of crystallinity being at the top of the tunnel barrierlayer.

In yet another general embodiment, an apparatus includes an array ofmagnetic tunnel junction devices arranged along a tape bearing surfaceof a magnetic tape head module, each magnetic tunnel junction devicehaving a reference layer, a free layer, and a tunnel barrier layerbetween the free and reference layers, where the tunnel barrier layer isprimarily crystalline alumina. In addition, an upper surface of the freelayer or reference layer under each tunnel barrier layer has physicalcharacteristics of being cleaned at a milling angle of between 40 and 80degrees for a duration sufficient to remove an amorphous native oxidesublayer therefrom. Moreover, the physical characteristics includeabsence of a metal oxide along the upper surface having an oxygen tometal ratio in the metal oxide that is outside an approximatelystoichiometric ratio.

FIG. 1A illustrates a simplified tape drive 100 of a tape-based datastorage system, which may be employed in the context of the presentinvention. While one specific implementation of a tape drive is shown inFIG. 1A, it should be noted that the embodiments described herein may beimplemented in the context of any type of tape drive system.

As shown, a tape supply cartridge 120 and a take-up reel 121 areprovided to support a tape 122. One or more of the reels may form partof a removable cartridge and are not necessarily part of the system 100.The tape drive, such as that illustrated in FIG. 1A, may further includedrive motor(s) to drive the tape supply cartridge 120 and the take-upreel 121 to move the tape 122 over a tape head 126 of any type. Suchhead may include an array of readers, writers, or both.

Guides 125 guide the tape 122 across the tape head 126. Such tape head126 is in turn coupled to a controller 128 via a cable 130. Thecontroller 128, may be or include a processor and/or any logic forcontrolling any subsystem of the drive 100. For example, the controller128 typically controls head functions such as servo following, datawriting, data reading, etc. The controller 128 may include at least oneservo channel and at least one data channel, each of which include dataflow processing logic configured to process and/or store information tobe written to and/or read from the tape 122. The controller 128 mayoperate under logic known in the art, as well as any logic disclosedherein, and thus may be considered as a processor for any of thedescriptions of tape drives included herein, in various embodiments. Thecontroller 128 may be coupled to a memory 136 of any known type, whichmay store instructions executable by the controller 128. Moreover, thecontroller 128 may be configured and/or programmable to perform orcontrol some or all of the methodology presented herein. Thus, thecontroller 128 may be considered to be configured to perform variousoperations by way of logic programmed into one or more chips, modules,and/or blocks; software, firmware, and/or other instructions beingavailable to one or more processors; etc., and combinations thereof.

The cable 130 may include read/write circuits to transmit data to thehead 126 to be recorded on the tape 122 and to receive data read by thehead 126 from the tape 122. An actuator 132 controls position of thehead 126 relative to the tape 122.

An interface 134 may also be provided for communication between the tapedrive 100 and a host (internal or external) to send and receive the dataand for controlling the operation of the tape drive 100 andcommunicating the status of the tape drive 100 to the host, all as willbe understood by those of skill in the art.

FIG. 1B illustrates an exemplary tape cartridge 150 according to oneembodiment. Such tape cartridge 150 may be used with a system such asthat shown in FIG. 1A. As shown, the tape cartridge 150 includes ahousing 152, a tape 122 in the housing 152, and a nonvolatile memory 156coupled to the housing 152. In some approaches, the nonvolatile memory156 may be embedded inside the housing 152, as shown in FIG. 1B. In moreapproaches, the nonvolatile memory 156 may be attached to the inside oroutside of the housing 152 without modification of the housing 152. Forexample, the nonvolatile memory may be embedded in a self-adhesive label154. In one preferred embodiment, the nonvolatile memory 156 may be aFlash memory device, ROM device, etc., embedded into or coupled to theinside or outside of the tape cartridge 150. The nonvolatile memory isaccessible by the tape drive and the tape operating software (the driversoftware), and/or other device.

By way of example, FIG. 2 illustrates a side view of a flat-lapped,bi-directional, two-module magnetic tape head 200 which may beimplemented in the context of the present invention. As shown, the headincludes a pair of bases 202, each equipped with a module 204, and fixedat a small angle α with respect to each other. The bases may be“U-beams” that are adhesively coupled together. Each module 204 includesa substrate 204A and a closure 204B with a thin film portion, commonlyreferred to as a “gap” in which the readers and/or writers 206 areformed. In use, a tape 208 is moved over the modules 204 along a media(tape) bearing surface 209 in the manner shown for reading and writingdata on the tape 208 using the readers and writers. The wrap angle θ ofthe tape 208 at edges going onto and exiting the flat media supportsurfaces 209 are usually between about 0.1 degree and about 3 degrees.

The substrates 204A are typically constructed of a wear resistantmaterial, such as a ceramic. The closures 204B may be made of the sameor similar ceramic as the substrates 204A.

The readers and writers may be arranged in a piggyback or mergedconfiguration. An illustrative piggybacked configuration comprises a(magnetically inductive) writer transducer on top of (or below) a(magnetically shielded) reader transducer (e.g., a magnetoresistivereader, etc.), wherein the poles of the writer and the shields of thereader are generally separated. An illustrative merged configurationcomprises one reader shield in the same physical layer as one writerpole (hence, “merged”). The readers and writers may also be arranged inan interleaved configuration. Alternatively, each array of channels maybe readers or writers only. Any of these arrays may contain one or moreservo track readers for reading servo data on the medium.

FIG. 2A illustrates the tape bearing surface 209 of one of the modules204 taken from Line 2A of FIG. 2. A representative tape 208 is shown indashed lines. The module 204 is preferably long enough to be able tosupport the tape as the head steps between data bands.

In this example, the tape 208 includes 4 to 32 data bands, e.g., with 16data bands and 17 servo tracks 210, as shown in FIG. 2A on a one-halfinch wide tape 208. The data bands are defined between servo tracks 210.Each data band may include a number of data tracks, for example 1024data tracks (not shown). During read/write operations, the readersand/or writers 206 are positioned to specific track positions within oneof the data bands. Outer readers, sometimes called servo readers, readthe servo tracks 210. The servo signals are in turn used to keep thereaders and/or writers 206 aligned with a particular set of tracksduring the read/write operations.

FIG. 2B depicts a plurality of readers and/or writers 206 formed in agap 218 on the module 204 in Circle 2B of FIG. 2A. As shown, the arrayof readers and writers 206 includes, for example, 16 writers 214, 16readers 216 and two servo readers 212, though the number of elements mayvary. Illustrative embodiments include 8, 16, 32, 40, and 64 activereaders and/or writers 206 per array, and alternatively interleaveddesigns having odd numbers of reader or writers such as 17, 25, 33, etc.An illustrative embodiment includes 32 readers per array and/or 32writers per array, where the actual number of transducer elements couldbe greater, e.g., 33, 34, etc. This allows the tape to travel moreslowly, thereby reducing speed-induced tracking and mechanicaldifficulties and/or execute fewer “wraps” to fill or read the tape.While the readers and writers may be arranged in a piggybackconfiguration as shown in FIG. 2B, the readers 216 and writers 214 mayalso be arranged in an interleaved configuration. Alternatively, eacharray of readers and/or writers 206 may be readers or writers only, andthe arrays may contain one or more servo readers 212. As noted byconsidering FIGS. 2 and 2A-B together, each module 204 may include acomplementary set of readers and/or writers 206 for such things asbi-directional reading and writing, read-while-write capability,backward compatibility, etc.

FIG. 2C shows a partial tape bearing surface view of complementarymodules of a magnetic tape head 200 according to one embodiment. In thisembodiment, each module has a plurality of read/write (R/W) pairs in apiggyback configuration formed on a common substrate 204A and anoptional electrically insulative layer 236. The writers, exemplified bythe write transducer 214 and the readers, exemplified by the readtransducer 216, are aligned parallel to an intended direction of travelof a tape medium thereacross to form an R/W pair, exemplified by the R/Wpair 222. Note that the intended direction of tape travel is sometimesreferred to herein as the direction of tape travel, and such terms maybe used interchangeably. Such direction of tape travel may be inferredfrom the design of the system, e.g., by examining the guides; observingthe actual direction of tape travel relative to the reference point;etc. Moreover, in a system operable for bi-direction reading and/orwriting, the direction of tape travel in both directions is typicallyparallel and thus both directions may be considered equivalent to eachother.

Several R/W pairs 222 may be present, such as 8, 16, 32 pairs, etc. TheR/W pairs 222 as shown are linearly aligned in a direction generallyperpendicular to a direction of tape travel thereacross. However, thepairs may also be aligned diagonally, etc. Servo readers 212 arepositioned on the outside of the array of R/W pairs, the function ofwhich is well known.

Generally, the magnetic tape medium moves in either a forward or reversedirection as indicated by arrow 220. The magnetic tape medium and headassembly 200 operate in a transducing relationship in the mannerwell-known in the art. The piggybacked MR head assembly 200 includes twothin-film modules 224 and 226 of generally identical construction.

Modules 224 and 226 are joined together with a space present betweenclosures 204B thereof (partially shown) to form a single physical unitto provide read-while-write capability by activating the writer of theleading module and reader of the trailing module aligned with the writerof the leading module parallel to the direction of tape travel relativethereto. When a module 224, 226 of a piggyback head 200 is constructed,layers are formed in the gap 218 created above an electricallyconductive substrate 204A (partially shown), e.g., of AlTiC, ingenerally the following order for the R/W pairs 222: an insulating layer236, a first shield 232 typically of an iron alloy such as NiFe (—),cobalt zirconium tantalum (CZT) or Al—Fe—Si (Sendust), a sensor 234 forsensing a data track on a magnetic medium, a second shield 238 typicallyof a nickel-iron alloy (e.g., ˜80/20 at % NiFe, also known aspermalloy), first and second writer pole tips 228, 230, and a coil (notshown). The sensor may be of any known type, including those based onMR, GMR, AMR, tunneling magnetoresistance (TMR), etc.

The first and second writer poles 228, 230 may be fabricated from highmagnetic moment materials such as ˜45/55 NiFe. Note that these materialsare provided by way of example only, and other materials may be used.Additional layers such as insulation between the shields and/or poletips and an insulation layer surrounding the sensor may be present.Illustrative materials for the insulation include alumina and otheroxides, insulative polymers, etc.

The configuration of the tape head 126 according to one embodimentincludes multiple modules, preferably three or more. In awrite-read-write (W-R-W) head, outer modules for writing flank one ormore inner modules for reading. Referring to FIG. 3, depicting a W-R-Wconfiguration, the outer modules 252, 256 each include one or morearrays of writers 260. The inner module 254 of FIG. 3 includes one ormore arrays of readers 258 in a similar configuration. Variations of amulti-module head include a R-W-R head (FIG. 4), a R-R-W head, a W-W-Rhead, etc. In yet other variations, one or more of the modules may haveread/write pairs of transducers. Moreover, more than three modules maybe present. In further approaches, two outer modules may flank two ormore inner modules, e.g., in a W-R-R-W, a R-W-W-R arrangement, etc. Forsimplicity, a W-R-W head is used primarily herein to exemplifyembodiments of the present invention. One skilled in the art apprisedwith the teachings herein will appreciate how permutations of thepresent invention would apply to configurations other than a W-R-Wconfiguration.

FIG. 5 illustrates a magnetic head 126 according to one embodiment ofthe present invention that includes first, second and third modules 302,304, 306 each having a tape bearing surface 308, 310, 312 respectively,which may be flat, contoured, etc. Note that while the term “tapebearing surface” appears to imply that the surface facing the tape 315is in physical contact with the tape bearing surface, this is notnecessarily the case. Rather, only a portion of the tape may be incontact with the tape bearing surface, constantly or intermittently,with other portions of the tape riding (or “flying”) above the tapebearing surface on a layer of air, sometimes referred to as an “airbearing”. The first module 302 will be referred to as the “leading”module as it is the first module encountered by the tape in a threemodule design for tape moving in the indicated direction. The thirdmodule 306 will be referred to as the “trailing” module. The trailingmodule follows the middle module and is the last module seen by the tapein a three module design. The leading and trailing modules 302, 306 arereferred to collectively as outer modules. Also note that the outermodules 302, 306 will alternate as leading modules, depending on thedirection of travel of the tape 315.

In one embodiment, the tape bearing surfaces 308, 310, 312 of the first,second and third modules 302, 304, 306 lie on about parallel planes(which is meant to include parallel and nearly parallel planes, e.g.,between parallel and tangential as in FIG. 6), and the tape bearingsurface 310 of the second module 304 is above the tape bearing surfaces308, 312 of the first and third modules 302, 306. As described below,this has the effect of creating the desired wrap angle α₂ of the taperelative to the tape bearing surface 310 of the second module 304.

Where the tape bearing surfaces 308, 310, 312 lie along parallel ornearly parallel yet offset planes, intuitively, the tape should peel offof the tape bearing surface 308 of the leading module 302. However, thevacuum created by the skiving edge 318 of the leading module 302 hasbeen found by experimentation to be sufficient to keep the tape adheredto the tape bearing surface 308 of the leading module 302. The trailingedge 320 of the leading module 302 (the end from which the tape leavesthe leading module 302) is the approximate reference point which definesthe wrap angle α₂ over the tape bearing surface 310 of the second module304. The tape stays in close proximity to the tape bearing surface untilclose to the trailing edge 320 of the leading module 302. Accordingly,read and/or write elements 322 may be located near the trailing edges ofthe outer modules 302, 306. These embodiments are particularly adaptedfor write-read-write applications.

A benefit of this and other embodiments described herein is that,because the outer modules 302, 306 are fixed at a determined offset fromthe second module 304, the inner wrap angle α₂ is fixed when the modules302, 304, 306 are coupled together or are otherwise fixed into a head.The inner wrap angle α₂ is approximately tan⁻¹(δ/W) where δ is theheight difference between the planes of the tape bearing surfaces 308,310 and W is the width between the opposing ends of the tape bearingsurfaces 308, 310. An illustrative inner wrap angle α₂ is in a range ofabout 0.3° to about 1.1°, though can be any angle required by thedesign.

Beneficially, the inner wrap angle α₂ on the side of the module 304receiving the tape (leading edge) will be larger than the inner wrapangle α₃ on the trailing edge, as the tape 315 rides above the trailingmodule 306. This difference is generally beneficial as a smaller α₃tends to oppose what has heretofore been a steeper exiting effectivewrap angle.

Note that the tape bearing surfaces 308, 312 of the outer modules 302,306 are positioned to achieve a negative wrap angle at the trailing edge320 of the leading module 302. This is generally beneficial in helpingto reduce friction due to contact with the trailing edge 320, providedthat proper consideration is given to the location of the crowbar regionthat forms in the tape where it peels off the head. This negative wrapangle also reduces flutter and scrubbing damage to the elements on theleading module 302. Further, at the trailing module 306, the tape 315flies over the tape bearing surface 312 so there is virtually no wear onthe elements when tape is moving in this direction. Particularly, thetape 315 entrains air and so will not significantly ride on the tapebearing surface 312 of the third module 306 (some contact may occur).This is permissible, because the leading module 302 is writing while thetrailing module 306 is idle.

Writing and reading functions are performed by different modules at anygiven time. In one embodiment, the second module 304 includes aplurality of data and optional servo readers 331 and no writers. Thefirst and third modules 302, 306 include a plurality of writers 322 andno data readers, with the exception that the outer modules 302, 306 mayinclude optional servo readers. The servo readers may be used toposition the head during reading and/or writing operations. The servoreader(s) on each module are typically located towards the end of thearray of readers or writers.

By having only readers or side by side writers and servo readers in thegap between the substrate and closure, the gap length can besubstantially reduced. Typical heads have piggybacked readers andwriters, where the writer is formed above each reader. A typical gap is20-35 microns. However, irregularities on the tape may tend to droopinto the gap and create gap erosion. Thus, the smaller the gap is thebetter. The smaller gap enabled herein exhibits fewer wear relatedproblems.

In some embodiments, the second module 304 has a closure, while thefirst and third modules 302, 306 do not have a closure. Where there isno closure, preferably a hard coating is added to the module. Onepreferred coating is diamond-like carbon (DLC).

In the embodiment shown in FIG. 5, the first, second, and third modules302, 304, 306 each have a closure 332, 334, 336, which extends the tapebearing surface of the associated module, thereby effectivelypositioning the read/write elements away from the edge of the tapebearing surface. The closure 332 on the second module 304 can be aceramic closure of a type typically found on tape heads. The closures334, 336 of the first and third modules 302, 306, however, may beshorter than the closure 332 of the second module 304 as measuredparallel to a direction of tape travel over the respective module. Thisenables positioning the modules closer together. One way to produceshorter closures 334, 336 is to lap the standard ceramic closures of thesecond module 304 an additional amount. Another way is to plate ordeposit thin film closures above the elements during thin filmprocessing. For example, a thin film closure of a hard material such asSendust or nickel-iron alloy (e.g., 45/55) can be formed on the module.

With reduced-thickness ceramic or thin film closures 334, 336 or noclosures on the outer modules 302, 306, the write-to-read gap spacingcan be reduced to less than about 1 mm, e.g., about 0.75 mm, or 50% lessthan commonly-used LTO tape head spacing. The open space between themodules 302, 304, 306 can still be set to approximately 0.5 to 0.6 mm,which in some embodiments is ideal for stabilizing tape motion over thesecond module 304.

Depending on tape tension and stiffness, it may be desirable to anglethe tape bearing surfaces of the outer modules relative to the tapebearing surface of the second module. FIG. 6 illustrates an embodimentwhere the modules 302, 304, 306 are in a tangent or nearly tangent(angled) configuration. Particularly, the tape bearing surfaces of theouter modules 302, 306 are about parallel to the tape at the desiredwrap angle α₂ of the second module 304. In other words, the planes ofthe tape bearing surfaces 308, 312 of the outer modules 302, 306 areoriented at about the desired wrap angle α₂ of the tape 315 relative tothe second module 304. The tape will also pop off of the trailing module306 in this embodiment, thereby reducing wear on the elements in thetrailing module 306. These embodiments are particularly useful forwrite-read-write applications. Additional aspects of these embodimentsare similar to those given above.

Typically, the tape wrap angles may be set about midway between theembodiments shown in FIGS. 5 and 6.

FIG. 7 illustrates an embodiment where the modules 302, 304, 306 are inan overwrap configuration. Particularly, the tape bearing surfaces 308,312 of the outer modules 302, 306 are angled slightly more than the tape315 when set at the desired wrap angle α₂ relative to the second module304. In this embodiment, the tape does not pop off of the trailingmodule, allowing it to be used for writing or reading. Accordingly, theleading and middle modules can both perform reading and/or writingfunctions while the trailing module can read any just-written data.Thus, these embodiments are preferred for write-read-write,read-write-read, and write-write-read applications. In the latterembodiments, closures should be wider than the tape canopies forensuring read capability. The wider closures may require a widergap-to-gap separation. Therefore a preferred embodiment has awrite-read-write configuration, which may use shortened closures thatthus allow closer gap-to-gap separation.

Additional aspects of the embodiments shown in FIGS. 6 and 7 are similarto those given above.

A 32 channel version of a multi-module head 126 may use cables 350having leads on the same or smaller pitch as current 16 channelpiggyback LTO modules, or alternatively the connections on the modulemay be organ-keyboarded for a 50% reduction in cable span. Over-under,writing pair unshielded cables may be used for the writers, which mayhave integrated servo readers.

The outer wrap angles α₁ may be set in the drive, such as by guides ofany type known in the art, such as adjustable rollers, slides, etc. oralternatively by outriggers, which are integral to the head. Forexample, rollers having an offset axis may be used to set the wrapangles. The offset axis creates an orbital arc of rotation, allowingprecise alignment of the wrap angle α₁.

To assemble any of the embodiments described above, conventional u-beamassembly can be used. Accordingly, the mass of the resultant head may bemaintained or even reduced relative to heads of previous generations. Inother approaches, the modules may be constructed as a unitary body.Those skilled in the art, armed with the present teachings, willappreciate that other known methods of manufacturing such heads may beadapted for use in constructing such heads. Moreover, unless otherwisespecified, processes and materials of types known in the art may beadapted for use in various embodiments in conformance with the teachingsherein, as would become apparent to one skilled in the art upon readingthe present disclosure.

In an effort to improve data density in magnetic tape recording,magnetic tunnel valve read sensors are being investigated due to theirincreased magnetic sensitivity. Particularly, tunnel valve read sensorsusing MgO tunnel barrier layers have been considered. MgO produces alarge magnetoresistive (MR) effect (deltaR/R), which is severalfoldlarger than in GMR structures. MgO provides an MR effect ofapproximately 110 to 220%. However, MgO tunnel barrier layers have beenfound to be susceptible to dissolution in the presence of water. This isimportant for some applications, such as magnetic tape recording, wheresensors may be exposed to humidity in the environment. Dissolution ofthe tunnel barrier layer may affect resistance across the tunneljunction and in general may degrade tunneling, which in turn reducessignal, and can even render the head inoperable.

Tunnel junction devices having amorphous barriers of AlOx and TiOx havebeen used. However, their MR effect of only up to about 70% issignificantly lower than MgO (up to 220%), and therefore were replacedby MgO.

Various embodiments described herein implement crystalline alumina inthe tunnel barrier layer, because the crystalline alumina is lesssusceptible to dissolution in aqueous environments than MgO. Moreover,using the teachings found herein, the crystalline alumina can be formedat temperatures suitable for magnetic head processing.

Previous methods used for producing hard alumina generally requiretemperatures that exceed normal head processing temperatures, which canbe as low as about 200° C. to about 250° C. Thus, producing hard aluminafilms and layers in a magnetic head using such prior methods damages thedevices of the head, such as read transducers and write transducers.

FIG. 8 depicts an apparatus 800, in accordance with one embodiment. Asan option, the present apparatus 800 may be implemented in conjunctionwith features from any other embodiment listed herein, such as thosedescribed with reference to the other FIGS. Of course, however, suchapparatus 800 and others presented herein may be used in variousapplications and/or in permutations which may or may not be specificallydescribed in the illustrative embodiments listed herein. Further, theapparatus 800 presented herein may be used in any desired environment.

The apparatus 800 includes a magnetic tunnel junction device 802 havinga reference layer 804, a free layer 808, and a tunnel barrier layer 806therebetween, the tunnel barrier layer 806 comprising crystallinealumina.

In one embodiment, the apparatus may include a magnetic read sensor,where the magnetic tunnel junction device is a portion of the magneticread sensor. For example, the magnetic read sensor may be part of amagnetic head, e.g., a tape head as shown in FIGS. 1A, 2, and 5-7.

In some embodiments, only one magnetic tunnel junction device 802 ispresent in the apparatus. In other embodiments, a plurality of themagnetic tunnel junction devices may be present in the apparatus. Forexample, an array of magnetic tunnel junction devices 802 may be presenton a common substrate. For example, in magnetic head, the array may be alinear array of read sensors on a common substrate, which together arepart of a module of a magnetic tape head. See, e.g., the array orreaders 216 of FIG. 2B.

The apparatus may be a tape drive, e.g., as shown in FIG. 1A, therebyincluding a drive mechanism for passing a magnetic recording tape overthe magnetic tunnel junction device, and a controller electricallycoupled to the magnetic tunnel junction device.

In another embodiment, the magnetic tunnel junction device is a portionof a magnetic random access memory device, e.g., of conventionalconstruction except for having the tunnel barrier layer(s) ofcrystalline alumina.

With continued reference to FIG. 8, the reference layer 804 may be of amagnetic material such as CoFe, CoFeB, etc., or any other suitablemagnetic material, as would be apparent to one skilled in the art uponreading the present disclosure. The free layer may be comprised of filmsof CoFe(B), CoFe, NiFe, etc. The reference layer 804 and free layer 808may be formed using known techniques. Moreover, while the referencelayer 804 is shown formed below the tunnel barrier layer 806, it mayalso equivalently be formed above the tunnel barrier layer 806.

The tunnel barrier layer 806 is primarily crystalline alumina, i.e.,alumina that is at least partially poly-crystalline such that thedensity increase due to crystallinity is at least 30% greater thanpurely amorphous alumina of the same chemical composition andapproximate thickness. Ideally, the tunnel barrier layer 806 is fullycrystalline.

With continued reference to FIG. 8, preferably, electrodes 810, 812 ofconventional construction may be provided to enable passage of a currentthrough the magnetic tunnel junction device 802. In some embodiments,the electrodes may be in electrical communication with a circuit 814that processes a signal from the magnetic tunnel junction device 802,such signal being derived from a current passing through the magnetictunnel junction device 802 from one electrode to the other in adirection perpendicular to the plane of deposition of the tunnel barrierlayer 806. Examples of such a circuit 814 include a read channel wherethe magnetic tunnel junction device 802 is part of a read sensor, acontroller where the magnetic tunnel junction device 802 is part of amagnetic random access memory device, etc.

FIG. 9 illustrates an exemplary structure 900 for a tunnelingmagnetoresistive read sensor according to one exemplary embodiment. Asan option, the present structure 900 may be implemented in conjunctionwith features from any other embodiment listed herein, such as thosedescribed with reference to the other FIGS. Of course, however, suchstructure 900 and others presented herein may be used in variousapplications and/or in permutations which may or may not be specificallydescribed in the illustrative embodiments listed herein. Further, thestructure 900 presented herein may be used in any desired environment.

The structure 900 of FIG. 9 is formed from the bottom upward, startingwith Ta and Ru underlayers 904, 906 formed on a substrate such as alower magnetic shield 902. An antiferromagnetic layer 908 is formedthereover, followed by an antiparallel pinned layer structure havingCoFe layers 910, 914 separated by a thin, e.g., approximately 4 or 8angstrom thick antiparallel coupling layer 912 of Ru. A tunnel barrierlayer 916 of crystalline alumina is formed above the pinned layerstructure. A bi-layer free layer having CoFe and NiFe layers 918, 920 isformed above the tunnel barrier layer 916. A cap layer of Ru, Ta and Rulayers 922, 924, 926 are formed above the free layer.

Now referring to FIG. 10, a flowchart of a method 1000 is shownaccording to one embodiment. The method 1000 may be used to create anyof the various embodiments depicted in FIGS. 1-9, among others, invarious embodiments. Of course, more or less operations than thosespecifically described in FIG. 10 may be included in method 1000, aswould be understood by one of skill in the art upon reading the presentdescriptions.

Each of the steps of the method 1000 may be performed using knowntechniques according to the teachings herein.

As shown in FIG. 10, method 1000 includes forming a first magnetic layerin step 1002. The first magnetic layer may be a reference layer, a freelayer, etc.

In optional step 1004, a preparatory process may be performed to preparethe upper surface of the first magnetic layer for formation of thetunnel barrier layer thereon. The upper surface of the first magneticlayer is cleaned by milling, e.g., sputter cleaning, bombarding withionized argon, etc. the upper surface of the first magnetic layer at anangle of between 40 and 80 degrees from normal to the upper surface,preferably at an angle of about 60 degrees. Moreover, a duration of thecleaning is preferably sufficient to remove an amorphous native oxidesublayer of the first magnetic layer, e.g., an amorphous CoFeO_(x) layerwhere x in this and other layers represents a potential deviation froman approximately stoichiometric ratio, which can degrade the adhesion ofthe overlying layer. As general guidance, the upper surface of the firstmagnetic layer should be substantially free of the amorphous nativeoxide sublayer after the milling. In general, the cleaning step may takeapproximately 10 seconds. An oxygen plasma may then be applied for atleast one of removing carbonaceous contaminants and oxidizing the uppersurface of the first magnetic layer, e.g., to reoxidize reduced metaloxides. The sputtering energy during the milling may be in a range ofabout 250 to about 500 eV. Where the first magnetic layer is CoFe, forexample, reoxidation is exothermic and promotes CoFe-oxiderecrystallization on the underlying CoFe grains. Newly formed oxidecrystallites act as template for subsequent alumina coatingcrystallization. The cleaning promotes formation of a graded transitionlayer between the first magnetic layer and the subsequently-formedcrystalline alumina layer thereabove.

FIG. 11A is a magnified view of a properly formed, graded, CoFeAlO_(x)transition layer, with substantially no amorphous CoFeO_(x) at the CoFeinterface. The composition of the graded CoFeAlO_(x) transition layerthus transitions from a higher CoFe content at the left side to a higheralumina content on the right side in the direction of the arrow of FIG.11B, which is a Z-contrast image of the structure in FIG. 11A with thespectral scan direction being indicated by the arrow. FIG. 11C is anelectron energy loss spectroscopy (EELS) scan across the layer interfaceshown in FIGS. 11A and 11B. The EELS scan shows the presence of thegraded interface. The alumina layer formed on the CoFe layer exhibited ahigh degree of crystallinity.

Referring to step 1006 of FIG. 10, a tunnel barrier layer is formedabove the first magnetic layer. Various formation methods may be used.The tunnel barrier layer is formed at a temperature of less than 100degrees centigrade, preferably less than about 50 degrees centigrade,and ideally at room temperature (in a range of 20-50 degreescentigrade).

In a first approach, an amorphous alumina layer is formed. Then, theamorphous alumina layer is irradiated to convert the amorphous aluminato crystalline alumina. Illustrative low temperature processes that maybe adapted for forming an amorphous alumina tunnel barrier layeraccording to the teachings herein are presented in US Patent Appl. Pub.No. 2014-0087089 A1 to Biskeborn et al., which is herein incorporated byreference.

Formation of the tunnel barrier layer may result in a physical gradientin the degree of crystallinity that increases from a bottom to a topthereof, with the highest degree of crystallinity being at the top ofthe layer, which receives the highest amount of exposure. The degree ofcrystallinity refers to the fraction of alumina that is crystalline. Thebottom is the lowermost layer deposited during formation of the tunnelbarrier layer. Moreover, a quality of the crystallinity of the aluminamay increase from a bottom to a top thereof. The quality of thecrystallinity refers to the degree of crystallographic orientation. Thehighest degree of crystallographic orientation is 100% of highly alignedpurely crystalline alumina. Post exposure thermal anneal may be used topromote uniformity of crystallinity throughout the barrier layer.

In another approach, the tunnel barrier layer may be formed using thelow-temperature processes disclosed in U.S. Pat. No. 8,526,137 toBiskeborn et al., which is herein incorporated by reference.

In another approach, forming the tunnel barrier layer includes sputterdepositing (sputtering) aluminum under conditions that result indeposition of crystalline alumina. The sputtering is performed using analuminum target, and oxygen is added during the sputtering.

In another approach, forming the tunnel barrier layer includes sputterdepositing alumina from an alumina target under conditions that resultin deposition of crystalline alumina.

Referring again to FIG. 10, step 1008 includes forming a second magneticlayer above the tunnel barrier layer. As in step 1002, known techniquesmay be used to form the second magnetic layer.

It will be clear that the various features of the foregoing systemsand/or methodologies may be combined in any way, creating a plurality ofcombinations from the descriptions presented above.

It will be further appreciated that embodiments of the present inventionmay be provided in the form of a service deployed on behalf of acustomer.

The inventive concepts disclosed herein have been presented by way ofexample to illustrate the myriad features thereof in a plurality ofillustrative scenarios, embodiments, and/or implementations. It shouldbe appreciated that the concepts generally disclosed are to beconsidered as modular, and may be implemented in any combination,permutation, or synthesis thereof. In addition, any modification,alteration, or equivalent of the presently disclosed features,functions, and concepts that would be appreciated by a person havingordinary skill in the art upon reading the instant descriptions shouldalso be considered within the scope of this disclosure.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. Thus, the breadth and scope of an embodiment of the presentinvention should not be limited by any of the above-described exemplaryembodiments, but should be defined only in accordance with the followingclaims and their equivalents.

What is claimed is:
 1. A method, comprising: forming a first magneticlayer; forming a tunnel barrier layer above the first magnetic layer;and forming a second magnetic layer above the tunnel barrier layer, thetunnel barrier layer comprising crystalline alumina, the tunnel barrierlayer being formed at a temperature of less than 100 degrees centigrade.2. A method as recited in claim 1, wherein the tunnel barrier layerbeing formed at a temperature of between about 20 and about 50 degreescentigrade.
 3. A method as recited in claim 1, wherein forming thetunnel barrier layer includes: forming an amorphous alumina layer; andirradiating the amorphous alumina layer to convert the amorphous aluminato crystalline alumina.
 4. A method as recited in claim 3, comprisingpreparing an upper surface of the first magnetic layer prior to formingthe tunnel barrier layer on the upper surface of the first magneticlayer, the preparing comprising: cleaning by milling the upper surfaceof the first magnetic layer at an angle of between 50 and 70 degreesfrom normal to the upper surface; and applying an oxygen plasma for atleast one of removing carbonaceous contaminants and oxidizing the uppersurface of the first magnetic layer.
 5. A method as recited in claim 4,wherein a sputtering energy is in a range of about 250 to about 500 eV.6. A method as recited in claim 4, wherein a duration of the cleaning issufficient to remove an amorphous native oxide sublayer of the firstmagnetic layer.
 7. A method as recited in claim 1, wherein forming thetunnel barrier layer includes: sputter depositing at least one ofaluminum and alumina under conditions that result in deposition ofcrystalline alumina.
 8. A method as recited in claim 7, comprisingpreparing an upper surface of the first magnetic layer prior to formingthe tunnel barrier layer on the upper surface of the first magneticlayer, the preparing comprising: cleaning by milling the upper surfaceof the first magnetic layer at an angle of between 50 and 70 degreesfrom normal to the upper surface; and applying an oxygen plasma for atleast one of removing carbonaceous contaminants and oxidizing the uppersurface of the first magnetic layer.
 9. A method as recited in claim 8,wherein a sputtering energy is in a range of about 250 to about 500 eV,wherein a duration of the cleaning is sufficient to remove an amorphousnative oxide sublayer of the first magnetic layer.
 10. A method asrecited in claim 7, wherein the sputter depositing uses an aluminumtarget, and comprising adding oxygen during the sputtering.
 11. A methodas recited in claim 7, wherein the sputter depositing uses an aluminatarget.
 12. An apparatus, comprising: an array of magnetic tunneljunction devices arranged along a tape bearing surface of a magnetictape head module, each magnetic tunnel junction device having areference layer, a free layer, and a tunnel barrier layer between thefree and reference layers, wherein the tunnel barrier layer of eachmagnetic tunnel junction device is primarily crystalline alumina,wherein each tunnel barrier layer has a physical gradient in a degree ofcrystallinity that increases from a bottom to a top thereof, with thehighest degree of crystallinity being at the top of the tunnel barrierlayer.
 13. An apparatus as recited in claim 12, wherein substantially noamorphous native oxide sublayer is present between each tunnel barrierlayer and a layer immediately thereunder.
 14. An apparatus as recited inclaim 12, wherein the tunnel barrier layer is formed on the referencelayer, the reference layer being of CoFe(B), wherein a graded transitionlayer of CoFeAlO_(x) is formed between the CoFe(B) reference layer andthe alumina tunnel barrier layer.
 15. An apparatus as recited in claim12, wherein the tunnel barrier layer is formed on the reference layer,the reference layer being of CoFe, wherein a graded transition layer ofCoFeAlO_(x) is formed between the CoFe reference layer and the aluminatunnel barrier layer.
 16. An apparatus, comprising: an array of magnetictunnel junction devices arranged along a tape bearing surface of amagnetic tape head module, each magnetic tunnel junction device having areference layer, a free layer, and a tunnel barrier layer between thefree and reference layers, wherein the tunnel barrier layer of eachmagnetic tunnel junction device is primarily crystalline alumina,wherein an upper surface of the free layer or reference layer under eachtunnel barrier layer has physical characteristics of being cleaned at amilling angle of between 40 and 80 degrees for a duration sufficient toremove an amorphous native oxide sublayer therefrom, wherein thephysical characteristics include absence of a metal oxide along theupper surface having an oxygen to metal ratio in the metal oxide that isoutside an approximately stoichiometric ratio.
 17. An apparatus asrecited in claim 16, wherein the upper surface of the free layer orreference layer under each tunnel barrier layer has physicalcharacteristics of oxygen exposure prior to formation of the tunnelbarrier layer thereabove.
 18. An apparatus as recited in claim 17,wherein the physical characteristics of oxygen exposure include presenceof metal oxide crystallites.
 19. An apparatus as recited in claim 18,wherein each tunnel barrier layer includes a graded transition layer ofalumina with the metals in the free layer or reference layer under thetunnel barrier layer.